Although the present invention has application to forward-fold implements in general and to agricultural planters other than row crop planters (for example, it has application to grain drills), it will be discussed, for the most part, in connection with a row crop planter. Persons skilled in the art will readily appreciate that grain drills may be mounted on the planter frame in place of the row units, and that other ground-engaging tools, particularly cultivating tools, fertilizer applicators and tillage tools, may be substituted for the row units.
As agricultural planters became larger in width in the planting or field-use position, it became desirable to provide some mechanism to fold the planter for transport or storage. Many proposals have been provided for including, as a part of the main support frame for the implement, wing frames which hinge about their inner ends to swing or "fold" forwardly. That is, the outermost ends of the wing frames swing toward the tractor so that the wings, in the folded position, are parallel to each other and extend in the fore-to-aft direction. Some of these planter frames were provided with a fixed center section mounted to the main wheel set, and first and second wing sections mounted to hinge about the outboard ends of the center section, as in U.S. Pat. No. 4,137,852. In others, the wings extend to the center of the draft frame so that there is no fixed center sections, and the wings pivot about locations near the center of the longitudinal or draft frame, as in U.S. Pat. No. 4,319,643.
Subsequent improvements in forward-fold implement frames (sometimes called "carrier" frames) placed the pivot points for the wing sections at offset locations. That is, one pivot point was located forwardly relative to the other and closer to the centerline of the implement, so that the wing support wheels can be mounted in front of the wing frames in the field-use position; and, when the wings are folded, the wing support wheels interleave with one another due to the offset pivot arrangement. This reduces the transport width and is particularly useful for grain drills and the like, such as are disclosed in U.S. Pat. Nos. 4,763,915 and 5,024,279.
In these prior implement frames having forward-folding wing sections, when the wing sections are folded, the center of gravity of the wing sections is moved forwardly of the main wheel set normally located at the rear of the main, longitudinal frame. Moreover, most forward-fold wing sections provide some arrangement for securing the forward ends of the wing sections in the folded position to the main frame so that the forward ends of the wings, including all units carried by the wings, is supported by the main longitudinal frame. Both of these characteristics (that is, forward shifting of the center of gravity upon folding and supporting the forward ends of the wing sections on the center frame for transport), greatly increase the downward load on the tractor drawbar.
This drawbar loading problem is exacerbated as implements become larger and planters become wider because the folded length likewise becomes longer.